Refractory brain edema is a state of severe, progressive, and diffuse cerebral edema that causes rapid clinical deterioration, and does not generally respond to aggressive medical treatment. Refractory brain edema is usually seen after severe head injury, subarachnoid hemorrhage due to ruptured cerebral aneurysms, extensive brain infarction, and sometimes after excision of brain tumors. Despite advances in understanding, monitoring, and treatment, the outcome of patients with refractory brain edema remains poor with substantial mortality, severe and moderate disability rates, and corresponding low rates of successful outcomes.
The concept of wide bone removal for treatment of intracranial hypertension has been recognized since the nineteenth century. Different types of decompressive craniectomy have been described, including unilateral or bilateral frontal and subtemporal decompression and circumferential hemicraniectomy. Recently, bifrontal decompressive craniotomy has been used at increasing rates to treat refractory brain edema. Reasons for the increased use of bifrontal decompressive craniotomy include: 1) quickly lowers intracranial pressure to normal levels; 2) adds a vector of expansion to both cerebral hemispheres that may relieve subfalcine and transtentorial brain herniation; 3) quickly improves the partial pressure of brain tissue oxygen; 4) allows exploration of the subdural space on both sides of the cranium; and 5) allows quick tapering of the medical treatment (hypothermia, barbiturates, osmotic diuretics, ventriculostomy, prolonged hyperventilation, and hypertonic saline) to minimize side effects.
Preservation of bone flaps in a good and viable condition after a bifrontal decompressive craniotomy represents a formidable challenge. Currently, preservation of bone flaps in a good and viable condition is only possible by keeping the bone inside the body, such as under the skin of the abdominal wall or the thigh. The large size and round shape of the forehead bone, however, may exclude these sites even after breaking the bone into smaller pieces. The reconstruction of the resulting huge skull defect from the bifrontal decompressive craniotomy may only be possible by use of the patient's own bone. Using synthetic materials, like ceramic bone and custom bone, are very expensive. Furthermore, restoration of the normal shape and contour of the forehead is difficult using synthetic materials. Ideal cranioplasty materials should have maximal biocompatibility, low cost, low incidence of complications, wide accessibility, and ease of use. Autologous bone is considered the best material for cranioplasty; however, preservation of the bone entails morbidity related to the donor area, lengthening of the surgical procedure, and limited amount of bone that can be used for grafting.
Cranioplasty following an extended decompressive craniectomy is a formidable challenge, and its complexity increases with the size of the bone defect. Re-implantation of a patient's own bone flap yields excellent cosmetic results, with short operation time and without needing extensive remodeling. Several techniques for in-vivo preservation of craniectomy bone flap currently exist. In-vivo preservation sites may include the anterior abdominal wall, the front of the thigh, and subgaleal spaces. These sites, however, are not suitable for the very large and rounded forehead bones. Alternatively, bone flaps may be preserved in a bone bank using deep freezing at temperatures of approximately −80° C. Sterilization techniques for these bone flaps may include autoclaving, gamma irradiation, ethylene oxide (EtO) gas, and/or hydrogen peroxide (H2O2). All the above methods of bone flap sterilization kill the bone and are associated with increased risk of bone resorption and infection after reimplantation into the donor patient.